This invention relates to rotary circuit breakers, and, more particularly to a Supplemental Trip Unit for Rotary Circuit Interrupters.
U.S. Pat. No. 4,616,198 entitled Contact Arrangement for a Current Limiting Circuit Breaker, describes an early use of a first and second pair of circuit breaker contacts arranged in series to substantially reduce the amount of current let-through upon the occurrence of an overcurrent condition.
When the contact pairs are arranged upon one movable contact arm such as described within U.S. Pat. No. 4,910,485 entitled Multiple Circuit Breaker with Double Breaker Rotary Contact, some means must be provided to insure that the opposing contact pairs open rapidly upon occurrence of a short circuit overcurrent condition within the protected circuit.
U.S. Pat. No. 4,672,501 entitled Circuit Breaker and Protective Relay Unit, describes electronic circuits employed to determine the occurrence of an overcurrent condition and current transformers are employed to sense circuit current. However, when rotary contacts are employed with electronic circuits, the current transformer cores can become saturated upon occurrence of a short circuit overcurrent and an auxiliary trip unit must be employed to insure short circuit overcurrent protection.
Short circuit overcurrent protection in rotary contact circuit breakers is described in U.S. Pat. No. 5,103,198 entitled Instantaneous Trip Device of a Circuit Breaker, wherein the overpressure developed within the circuit breaker arc chamber upon contact separation in one pole drives a piston against the operating mechanism trip bar to actuate contact separation in the remaining circuit breaker poles. It has since been determined that the overpressure response is sensitive to voltage levels upon arc occurrence, and less sensitive to short circuit current values.